Cretaceous-Paleogene paleoenvironmental changes in the Yezo basin, Northeast Japan.

日本东北部虾夷盆地白垩纪-古近纪古环境变迁。

基本信息

批准号：
17540441
负责人：
ANDO Hisao
金额：
$ 2.37万
依托单位：
Ibaraki University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2007
项目状态：
已结题

项目摘要

During 2005 to 2007 the Lower Cretaceous to Paleocene Yezo Group in Hokkaido and the Lower Cretaceous Miyako and Upper Cretaceous Kuji groups in the Pacific side of Tohoku, have been surveyed from viewpoints of sedimentary facies, megafossil and pollen biostratigraphy, biofacies and others.Our survey revealed that six depositional sequences showing shallow-marine coarsening-and showing show-upward facies successions, are traceable in the Campanian Hakobuchi Formation over the Nakagawa area, northern Hokkaido. In the uppermost Albian to Turonian Mikasa Formation distributed in central Hokkaido, a total of 12 fourth-order depositional sequences can be observed in the eastern limb of the Ikushunbetsu- Sorachi anticline area. Each of sequences 20 to 100 m thick constitutes inner to outer shelf bioturbated sandy mudstone in the lower part and shoreface fine/medium massive/hummocky to trough cross-stratified sandstone in the upper. Furthermore, three third-order depositional sequence sets fo … More r both of the Hakobuchi and Mikasa formations, can be identified through stacking patterns of the sequences. Those sequences and sequence sets seem to have formed by repetitive relative sea-level changes influenced by global eustacy, as typically exemplified in the Western Interior Cretaceous in North America. The high-resolution sequence stratigraphic framework enables reconstructing sedimentary history and paleogeography in the western margin of the Yezo basin. Molluscan fossil occurrences and their composition such as ammonoids, inoceramids and other bivalves within each sequence indicate the taphonomic relation between fossil habitats and depositional environments.In the Santonian to Campanian Kuji Group exposed along the north Sanriku Coast, the stratigraphic variation in pollen flora shows a hinterland paleovegetational change represented by increase of bisaccate pollen. The lateral variation suggests that distribution of plant communities would have been analogous to present-day vegetational variation in several tens kilometer scale. The integrated approach of palynology and sedimentary facies analysis illustrates detailed paleovegetation and fine-scale paleoclimatic fluctuations during Late Cretaceous. Less

2005年至2007年期间，从沉积相、巨型化石和花粉生物地层、生物相等角度对北海道的下白垩统至古新统虾夷群以及东北太平洋沿岸的下白垩统宫古群和上白垩统久慈群进行了调查。揭示了六个显示浅海粗化和显示向上相序列的沉积层序，北海道北部中川地区的坎帕阶箱渊组位于北海道中部的阿尔布阶至土伦阶三笠组中，在生春别-空知背斜区的东翼共观察到12个四级沉积层序。每个层序厚度为 20 至 100 m，下部和岸面均由内陆架至外陆架生物扰动砂质泥岩组成。此外，Hakobuchi 和 Mikasa 地层的三个三级沉积层序组可以通过这些层序的堆积模式来识别。层序集似乎是由受全球平衡影响的相对海平面变化形成的，典型的例子是北美西部内陆白垩纪。高分辨率层序地层框架使得重建成为可能。饕藏盆地西缘的沉积历史和古地理以及每个序列中的软体动物化石的出现及其组成，如菊石、inoceramids 和其他双壳类动物，表明了化石栖息地和沉积环境之间的埋藏学关系。在北三陆海岸，花粉植物区系的地层变化显示出腹地古植被变化，其特征是双囊花粉的增加。变化表明植物群落的分布类似于当今数十公里尺度的植被变化。孢粉学和沉积相分析的综合方法说明了白垩纪晚期的详细古植被和细尺度古气候波动。